Anomalously Blue Elliptical Galaxies in the Sloan Survey Mentor: Dr. Mike Fanelli, UNT Collaborators: Dr. Pam Marcum, TCU & NASA Headquarters Dr. Christian Aars, San Angelo State U. Curtis Mitchell Department of Physics University of North Texas March 31, 2005

Galaxies Elliptical galaxies are on the left side of the Hubble “tuning fork” Hubble’s Galaxy Classification Scheme Edwin Hubble ( )

Stars Formed when interstellar gas and dust clouds collapse and begin fusing hydrogen into helium Wide variations in mass, color, and size exist Sagittarius Star Cloud

Star-Forming Systems Optically appear blue Luminosity dominated by OB-type stars NGC 2997 NGC 3310

Blueness OB stars lie along the upper end of main sequence Mark the location of recent star formation NGC 3603 Hertzsprung-Russell Diagram

Blue Galaxies “Starburst” galaxies Causes of star formation –Galactic interactions NGC 4314 NGC 4038/4039

Typical Ellipticals “Old” red galaxies –Little or no star formation in the last several billion years –Spherically shaped M 87 M 49

Galactic Interactions Unlike stellar evolution, interactions are important to galactic evolution NGC 2207 & IC 2163

Origin of Ellipticals Origins not clear –Most likely formed from galactic mergers –Early ellipticals possibly came from collapsing proto-galactic clouds NGC 4038/4039 Compact Group

Blue Ellipticals Unusual objects –Probably late-stage mergers –Stars have “settled down” –Using up remaining gas and dust NGC 3921

Isolated Systems Merger and collapse scenarios can be tested by looking for isolated ellipticals –Most ellipticals are in dense galactic environments KIG 557

Isolated Ellipticals Marcum, et al examined a sample of nine isolated ellipticals –Contained two blue systems and two red, normal systems (possibly oldest pristine galaxies in universe)

Questions What is the nature of the blue systems? How do these objects fit into an evolutionary sequence?

Sloan Digital Sky Survey Contains luminosities and positions for 100 million plus objects Detailed mapping of one quarter of the sky We will use the Sloan Survey to search for blue ellipticals SDSS Survey Telescope (2.5 meters )

Sloan Information SDSS will provide ID, redshifts, images, and spectra for up to a million galaxies Sloan Filters: FilterWavelength (Angstroms) Ultraviolet (u)3543 Green (g)4770 Red (r)6231 Near Infrared (i)7625 Infrared (z)9134 Survey Telescope Primary Mirror

Search Criteria We will look for objects meeting the blueness and shape criteria

Research Method Data mining –New branch of research: Earth Sciences: Life Sciences: Astronomy:

Search Example Image of Haro 2 retrieved from Sloan Sky Server –Absolute blue magnitude ~ -18 –(B-V) color = (typical E’s are +0.9 to 1.0) –Class: intermediate luminosity elliptical with a blue core, probably with a starburst nucleus

Sources Animation – Images Anglo-Australian Observatory NOAO (National Optical Astronomy Observatory) Hubble Space Telescope Literature R. Michard and P. Prugniel, “Peculiarities and Populations in Elliptical Galaxies” Astronomy and Astrophysics Vol. 423 N. 3 L.M. Buson, F. Bertola, A. Bressan, D. Burstein, and M. Cappellari, “Is the giant elliptical galaxy NGC 5018 a post-merger remnant?” Astronomy and Astrophysics v. 423 N. 3 F. Bournard, F. Combes, and C.J. Jog, “Unequal-mass galaxy merger remnants: Spiral-like morphology but elliptical-like kinematics” Astronomy and Astrophysics, V. 418 N. 2 P.M. Marcum, C.E. Aars, M.N. Fanelli, “Early-Type Galaxies in Extremely Isolated Environments: Typical Ellipticals?” The Astronomical Journal, Vol. 127 pp Sloan Web Page: